1. Field of the Invention
The present invention relates to an undulator for use with a free-electron laser system, and in particular, to an electro-magnetic undulator and processes for fabricating the same.
2. Description of the Related Art
Conventional devices used for the decelerator/interaction region of a collimated X-Ray free electron laser (FEL) typically rely on chains of opposing permanent magnets with 1 cm to 10 cm characteristic length scales to extract keV energy photons from GeV (Gigaelectron volt) energy electrons. Such conventional undulators permit only a few 10s of periods of the undulator in a device that is several meters long. Further, the intense fields developed by the close spacing of 1 T to 10 T permanent magnets in conventional permanent magnet undulators generate enormous forces that require significant structural support. Such structural support may result in undulators that occupy a volume of greater than one cubic meter, and may weigh more than 10,000 kg. Further, the magnetic fields tend to be non-uniform. In certain conventional implementations, to achieve very large controllable and uniform fields, superconducting magnets are often used, requiring cryogenic cooling and ancillary support hardware. Such types of undulators are too large, heavy, and expensive for many types of applications.
Certain other undulator designs use expensive, hand assembled 100 micron scale wax-bound powder permanent magnets, magnetic fields induced by a high power laser, or betatron oscillators which use laser-plasma Wakefield accelerators to extract MeV energy photons from GeV energy electrons.
Conventional wax-bound hard micro-magnets typically have not been scaled below 100 microns, must be hand assembled, and have poor field uniformity due to limitations in the NiFeB microstructural grain size, the magnetic domain size, and thermal stability of the material.
Further, conventional laser-driven undulators may require very high intensity (100 TW/m2) to achieve 1 T magnetic fields in free space or intricate waveguide structures to control the light. Additionally, in order to achieve high intensities, conventional laser-driven undulators typically require a great deal of specialized optics, ancillary electronics, power, and space in order to focus a 1 kW 10.6 micron laser or the like.
Similar intensities may also be realized by micro-fabricated off-axis illuminated periodic cavities used as advanced deflection structures, but such structures are very challenging to implement and so tend to be impractical for typical applications.
Betatron oscillations in a laser-plasma Wakefield accelerator have been used for the undulating field, but conventionally cannot produce a sufficiently narrow spectral output. Further, filtering the laser spectrum from the 36% bandwidth, typical of betatron sources, to 0.1% bandwidth may reduce the brightness by 99.7%.
While the foregoing conventional undulators may have certain characteristics that are improvements over sintered ceramic permanent magnets, they do not present an adequate path for future scaling.